The invention relates to the field of to a method and apparatus for monitoring air pressure in vehicle tires. More particularly, the invention relates to an apparatus for automatically sensing tire pressure and methods for operating the apparatus.
Tire pressure sensors have long been used to sense the pressure of tires to indicate when the tire is below a predetermine tire pressure. These sensors use various means, typically diaphragms screwed into tire value stems and responsive to tire pressure for activating an electrical switch for generating an alarm. Various types of tire monitoring systems have been used to provide continuous vehicle tire pressure sensing and monitoring during vehicular operation. Such systems typically include a monitor located in the passenger compartment of the vehicle for receiving encoded transmitted signals for respective tires and for alerting the vehicular operator through the use of audio alarms and graphic display indicators. The ability to selectively sense the pressure of each tire is desirable so that the subject tire can then be inflated to proper air pressure levels for safety and long tire wear life. The tire sensors unidirectionally communicate with the monitor transmitting tire pressure values received and processed by the monitor. Hence, these systems typically have tire pressure sensors located on the valve stems for the respective tires each with an associated embedded transmitter for generating respective encoded signals identifying the tire. The cab mounted monitor has a receiver the graphic display for alerting the operator in the event of low tire pressures.
U.S. Pat. No. 4,814,745 issued to Wang on Mar. 12, 1989 discloses a cap like signal device attached to the tire for sensing tire pressure. The cap includes an electric alarming buzzer responsive to a disk actuated by pressure disadvantageously without a cab mounted monitor. The disk activates the buzzer when the tire pressure is too low. U.S. Pat. No. 4,814,744 issued to Collins on Mar. 21, 1989 discloses a low tire pressure warning system having a mechanical side wall sensor with and dash alarm disadvantageous connected by a cable. U.S. Pat. No. 4,804,808 issued to Dal Cero on Feb. 14, 1989 discloses a pressure sensing devices that senses low tire pressure and signal low pressure using a transmitter and cab mounted receiver. U.S. Pat. No. 4,694,273 issued to Franchino on Sep. 15, 1987 disclose a tire sensing device having a movable element which activates a radio transmitter signal received by a receiver in the passenger compartment to activate visual and acoustic alarms. U.S. Pat. No. 5,289,161 issued to Huang on Feb. 22, 1994 discloses a tire pressure sensor having a diaphragm in a casing. The spring loaded diaphragm is movable between two positions. A signal producing units is activated in response to the position of the diaphragm. The signal generated is an encoded modulated RF signal for communicating an alarm signal to a receiver that determines which tire is low and activates a corresponding indication to indicate which tire has low tire pressure. Fuses in the sensors are used to generate the respective codes to match indicators of a display. U.S. Pat. No. 5,694,111 issued to Huang on Dec. 2, 1997 discloses an encoder unitand transmitter circuit for a tire pressure sensor device for generating encoded RF signals received by a cab receiver operating a display units. U.S. Pat. No. 4,734,674 issued to Thomas on Mar. 29, 1988 also discloses a tire pressure sensing device that, upon low pressure, transmits an encoded signal to a cab receiver having a plurality of display indicators on a front panel that are selectively activated to indicate the respective tire. U.S. Pat. No. 4,737,760 issued to Huang on Apr. 12, 1988 discloses another valve stem tire pressure warning device having a pressure sensitive diaphragm and spring switch for activating a transmitter signal communicated to the cab monitor. U.S. Pat. No. 4,319,220 issued to Pappas on Mar. 9, 1982 disclose a system for monitoring tire pressure of the tires having respective transmitters communicating alarm signals to a receiver in the cab monitor. U.S. Pat. No. 5,001,457 issued to Wang teaches a cab mounted monitor having displays with a graphic display for visually indicating which tire is low through the use of digitally encoded signals transmitted between respective tire sensor transmitters and the cab mounted central receiver. U.S. Pat. No. 4,970,491 issued to Saint on Nov. 13, 1990 teaches the use of specially encoded signal for a fleet of vehicle so that the receivers of one fleet of vehicle will not be activated by encoded signal from a sensor in another fleet of vehicle.
Typically, these systems teach valve mounted tire pressure sensors responsive to respective tire pressures of the tires for generating respective encoded signals transmitted to receiver in a cab mounted monitor having graphic visual displays and or audio alarms for indicating which one of the tires has low tire pressure. Typically, these signal are modulated at a fix radio frequency. However, these teaching do not address the problem of interference between signals from sensor on the same vehicle, which signals are modulated at the same frequency resulting in poor reception by the receiver, which may cause a failure of the monitoring system that fails to provide the operator with expedient current tire pressure indications and alarms. Additionally, these prior systems do not enable easy methods of modifying the assignment between the tire positions and the respective code of the valve stem mounted sensors, for example, when the sensor is dysfunctional, lost or stolen. These and other disadvantages are solved or reduced using the invention.
An object of the invention is to provide a vehicular tire pressure monitoring system that synchronizes radio transmissions from tire sensors transmitters to reduce potential interference between simultaneously transmitted tire pressure signals from the tire pressure sensor transmitters located on respective tires.
Another object of the invention is to provide tire sensor motion detection switches for synchronizing tire pressure signal transmissions from respective tire pressure sensor transmitters to reduce potential interference between simultaneously transmitted tire pressure signals.
Still another object of the invention is to method for reassigning the tire pressure sensor identification codes to respective tire locations.
The present inventions are directed to a vehicular tire pressure monitoring system that time division synchronizes transmitted tire pressure signals from respective tire sensor modules to prevent the transmitted signals from the interfering with each other for improved tire pressure monitoring. Each tire sensor module is attached to the valve of a respective tire the tire sensor module includes a motion detector switch that is activated when the vehicle is in motion through rotating tires that spin the sensors. Upon the detection of motion, battery power is routed to sensor electronics so that the sensor is powered during vehicular motion but remains dormant during periods of inactive vehicular motion so as to conserve sensor battery power. Each sensor module is individually configured to transmit respective tire pressure signals, including encoded identification codes, at differing non-overlapping time intervals so that the transmitted signals are staggered over time for time division synchronization. As such, the signals are transmitted at different times so as to prevent cross interference between these signals thereby improving the reception of these signals by the receiver of the monitor in the passenger compartment.
In another aspect of the invention, the individual sensor modules can be activated preferably by vehicular motion to transmit the respective identification code signals received by the receiver in the monitor that is manually programmed into a code assignment mode that selects, using a display panel, the desired tire location and then assigns that tire location to the new identification code upon reception of the transmitted signal from a respective sensor module. This ability to reassign the sensor identification code enables the replacement of sensors that may have become defective, lost or stolen. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.